CRACK TIP DAMAGE AND CRAZING IN POLYMERS UNDER LOADING
受载高聚物裂尖的损伤和银纹化

In situ observation via SEM was conducted to study the crack-tip crazing damage process in polymers under loading. By considering the polymer bulk as linear viscoelastic body and the craze zone at crack tip as a nonlinear damage zone, the control equation for craze zone growth was derived. It is shown that for a time-independent craze-zone stress, the craze zone grows only if the crack-tip stress intensity factor is changed. If the crack-tip stress intensity factor remains constant during loading, the growth rate of the craze zone length will be interrelated to the crack-tip stress, the craze zone length and the rate of change of the craze-zone stress. If both the craze-zone stress and the crack-tip stress intensity factor are time-independent, the craze zone length will be constant during crack growth, which is the case of self-similar crack growth. Moreover, a new stress distribution model in craze zone was presented based on the constructed damage evolution law. The lengthening and thickening of the craze zone at a crack tip was formulated. The numerical calculations from the proposed model agree well with published experimental data.